The differential relay actually compares between primary therefore. Problem statement article pdf available in ieee transactions on power delivery 164. Within a very short time this relay detects faults occuring within the zone to be protected by. Type ca percentage differential relay for transformer protection. The highimpedance input is created by an internal impedance, typically resistive, of 2000 ohms or higher. The following are the classification of the differential protection relay. Modified differential ground fault protection keywords. Partial differential relaying powell industries, inc. Current differential line protection setting consideration.
Differential protection symposium belo horizontenovember 2005 g. The differential protection function protects the zone between the main and additional current sensors. Protection relays differential relays b high impedance differential protection. Pickup value id slope k1 slope k2 with footing point ir0 ires. With the differential protection relaying, the cts at both end of the stator windings must be same. Principles of differential relaying the restraint characteristic what needs to be realised is that the first one is properly termed the restraint characteristic rc whilst the latter is an operating characteristic. Abstractpercentage restrained differential protection is one of.
Modern line current differential protection solutions. Pdf high impedance restricted earth fault protection. Differential protection is applicable to all parts of the power system. The following safety and common symbols may be used in this manual and on. The percentage differential relay is defined as the relay that operates on the phase difference of two or more similar electrical quantities. Thus this scheme provides protection to the greater percentage of the stator winding. The mathematical relationship between differential protection and directional protection is derived. A new approach to current differential protection for transmission lines m. Scope this document introduces the application of the threephase differential protection in ref542plus.
Generator stator protection, underover voltage, under over. The percentage differential protection or merzprice protection based on the circulating current pronciple can also be used for the transformers. Protection devices for electrical systems minimize fault damages, assist in maintaining power system stability and help to limit supply interruptions to consumers. Pdf differential protection of power transformer in substation. Type ca percentage differential relay for transformer. To determine the correct tap setting, calculate the currents delivered to the relay at full load on the trans. Protection functions bias differential protection 87 harmonic restraint protection over fluxing i. The percentage differential relay is defined as the relay that operates on the phase difference of two or more similar electrical quantities exceeds a predetermined amount.
Figure 6basic relay connections one phase for fixed percentage restraint. Within the limits of the accuracy of the cts and the relays, true bus differential relaying will detect all faults on the protected bus. True bus differential relaying compares all currents entering and leaving a switchgear bus. Alexander ge corporate ge power management research and development malvern, pa schenectady, ny updated and presented by subhash c. The type ca percentage differential relay for trans former protection is designed for the protection of power transformer. Abstractline current differential protection creates challenges for relay design and application. Strictly speaking the rc tells us how much current a relay will use to restrain based on the currents.
Transformer differential protection percentage restraint differential protective relays have. The percentage restraint characteristic requires that the differential current be greater than a percentage of the through restraint current. Current differential line protection current differential relaying is a method of extending the benefits of differential protection as applied to transformers, buses or generators to the protection of transmission lines. Patel ge power management malvern, pa presented at the electric council of new england. Among them differential relay is very commonly used relay for protecting transformers and generators from localised faults. A new approach to current differential protection for. Percentage restrained differential relays measure the individual branch currents and quantify the through current in the zone of protection. The differential protection relay will pick up if magnitude of differential current is more than a fixed percentage of the restraining current. A currentbased solution for transformer differential protection part i. It is based on ampereturnbalance of all windings mounted on the same magnetic core lag. Differential protection for standard power transformers has been used for decades. This paper carries the idea of selection of dual slope differential relay parameters for various faulty conditions on the system. This system gives protection against phase to phase faults and phase to ground faults to the power transformers. Jan 14, 2017 a differential relay is defined as the relay that operates when the phase difference of two or more identical electrical quantities exceeds a predetermined amount.
This popular scheme is known as biased differential protection or merzprice protection. Jun 08, 2019 the relays used in power system protection are of different types. Sep 08, 2016 general scheme of differential protection 6. Evaluating the impact of increasing system fault currents on. Mdgf, ground fault, modified differential ground fault protection, created date. Modern line current differential protection solutions hank miller and john burger, american electric power normann fischer and bogdan kasztenny, schweitzer engineering laboratories, inc. For power transformers, it is recommended that percentage differential protection be provided for transformers rated kva and above if circuit breakers are provided for each winding into which power can flow when an internal fault occurs, and for all.
A sensitive current element in series with the highimpedance element is calibrated in volts based on the voltage drop across the internal impedance. The only difference between them is the restraining coil. When the relay is correctly set, one screw must be in the lower row of holes at the correct tap value and the other must be in the hole directly above. The slope characteristic provides high sensitivity when low levels of current. This basic percentage differential protection scheme forms the basis of the practically very commonly used percentage differential protection scheme for alternator stator windings. Principles of differential relaying the restraint characteristic suppose further that there is 0. Principle of percentage restrained differential protection. This report is to clarify the basic difference between the obsolete kd4 kd41 electromechanical relay and the present design kd10 kd11 compensator distance relays. The differential protection of power transformer is a unit protection scheme. The differential protection of transformer has many advantages over other schemes of protection. The bdd relays are specifically designed for transformer protection and include a sensitive. The differential protection is designed to protect power transformers or highvoltage motors. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. Line differential protection is a strict selective object protection.
Ziegler, 102005 page 19 id ir0 k1 k2 iop ires digital differential protection. Percentage differential protection for transformers your. Thompson, schweitzer engineering laboratories, inc. L to limit current through relay to may 15, 2018 generally differential protection is provided in the electrical power transformer rated more than 5mva. Basic percentage differential protection scheme for. Micro processor based advanced bus protection scheme using iec 61850 process bus 92 sampled values k. Pdf a currentbased solution for transformer differential. Problems for the differential protection caused by transformer inrush currents are discussed.
Percentage differential protection slope transformer scribd. Micro processor based advanced bus protection scheme using. In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected 4 the first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as overcurrent, overvoltage, reverse power flow, overfrequency, and underfrequency. It is used here to protect transformers from a few mva to several tens of mva from internal faults inside the protected zone between the two sets of cts. Setting procedures are only discussed in a general nature in the material to follow.
Principles of differential relaying my protection guide. Percentage differential protection slope in differential. Pdf optimizing differential protection settings for power. Bus protection, automatic reclosing, 292 by backup relays, 275, 291 circuitbreaker bypsasing, 292 combined power transformer and bus, 287 current differential with overcurrent relays, 278 current differential with overvoltage relays, 288 current differential with percentage relays, 284 directional comparison, 277 fault bus, 275 grounding. In modern numerical differential protection relay two. Let for differential protection to operate, id should be greater than the x% of ib. In percentage differential protection, we provide a slope feature to the differential protection relay. Differential protection for arbitrary 3ph power transformer. Differential protection of yy and connected power transformer mayurdhvajsinh p.
Comparing current flowing into a line to the current flowing out of the same line allows for a simple protection scheme. Percentage restrained differential, percentage of what. Principle of differential protection by the small percentage unbalance may be substantial. Percentage differential protection free download as word doc. It is a static device, totally enclosed and usually oil immersed, and. Percentage differential protection for transformers. Jul 06, 2016 to prevent the differential protection scheme from picking up under such conditions, a percentage differential protection scheme is used. Transformer protection application guide this guide focuses primarily on application of protective relays for the protection of power transformers, with an emphasis on the most prevalent protection schemes and transformers.
Differential relays are very sensitive to the faults occurred within the zone of protection but they are least sensitive to the faults. It is the advanced form of differential protection relay. Switchgear and protective devices 2015 8 p a g e risk of synchronous motors in large industrial premises falling out of step and tripping out. Abstractpercentage restrained differential protection is one of the oldest forms of adaptive protection algorithms. The faults occur in the transformer inside the insulating oil can be detected by buchholz relay. Differential protection of a transformer the transformer is one of the major equipment in power system.
The general layout of a protection system may be viewed as given in the following figure. Pdf easy method for testing transformer differential relays. The differential protection relay is used for the protection of the generator, transformer, feeder, large motor, busbars etc. Differential protection falls into one of the following three.